Detailed explanation of PHP thumbnail generation and image watermark creation

  /**
   * Image constructor.
   * @param string $imagePath 图片路径
   * @param string $markPath 水印图片路径
   * @param int $new_width 缩略图宽度
   * @param int $new_height 缩略图高度
   * @param int $quality JPG图片格输出质量
   */
  public function __construct(string $imagePath,
                string $markPath = null,
                int $new_width = null,
                int $new_height = null,
                int $quality = 75)
  {
    $this->imgPath = $_SERVER['DOCUMENT_ROOT'] . $imagePath;
    $this->waterMarkPath = $markPath;
    $this->newWidth = $new_width ? $new_width : $this->width;
    $this->newHeight = $new_height ? $new_height : $this->height;
    $this->quality = $quality ? $quality : 75;

    list($this->width, $this->height, $this->type) = getimagesize($this->imgPath);
    $this->img = $this->_loadImg($this->imgPath, $this->type);


    //生成缩略图
    $this->_thumb();
    //添加水印图片
    if (!empty($this->waterMarkPath)) $this->_addWaterMark();
    //输出图片
    $this->_outputImg();
  }

   /**
   * 缩略图(按等比例,根据设置的宽度和高度进行裁剪)
   */
  private function _thumb()
  {

    //如果原图本身小于缩略图，按原图长高
    if ($this->newWidth > $this->width) $this->newWidth = $this->width;
    if ($this->newHeight > $this->height) $this->newHeight = $this->height;

    //背景图长高
    $gd_width = $this->newWidth;
    $gd_height = $this->newHeight;

    //如果缩略图宽高，其中有一边等于原图的宽高，就直接裁剪
    if ($gd_width == $this->width || $gd_height == $this->height) {
      $this->newWidth = $this->width;
      $this->newHeight = $this->height;
    } else {

      //计算缩放比率
      $per = 1;

      if (($this->newHeight / $this->height) > ($this->newWidth / $this->width)) {
        $per = $this->newHeight / $this->height;
      } else {
        $per = $this->newWidth / $this->width;
      }

      if ($per < 1) {
        $this->newWidth = $this->width * $per;
        $this->newHeight = $this->height * $per;
      }
    }

    $this->newImg = $this->_CreateImg($gd_width, $gd_height, $this->type);
    imagecopyresampled($this->newImg, $this->img, 0, 0, 0, 0, $this->newWidth, $this->newHeight, $this->width, $this->height);
  }

   /**
   * 添加水印
   */
  private function _addWaterMark()
  {
    $ratio = 1 / 5; //水印缩放比率

    $Width = imagesx($this->newImg);
    $Height = imagesy($this->newImg);

    $n_width = $Width * $ratio;
    $n_height = $Width * $ratio;

    list($markWidth, $markHeight, $markType) = getimagesize($this->waterMarkPath);

    if ($n_width > $markWidth) $n_width = $markWidth;
    if ($n_height > $markHeight) $n_height = $markHeight;

    $Img = $this->_loadImg($this->waterMarkPath, $markType);
    $Img = $this->_thumb1($Img, $markWidth, $markHeight, $markType, $n_width, $n_height);
    $markWidth = imagesx($Img);
    $markHeight = imagesy($Img);
    imagecopyresampled($this->newImg, $Img, $Width - $markWidth - 10, $Height - $markHeight - 10, 0, 0, $markWidth, $markHeight, $markWidth, $markHeight);
    imagedestroy($Img);
  }

  /**
   * 缩略图(按等比例)
   * @param resource $img 图像流
   * @param int $width
   * @param int $height
   * @param int $type
   * @param int $new_width
   * @param int $new_height
   * @return resource
   */
  private function _thumb1($img, $width, $height, $type, $new_width, $new_height)
  {

    if ($width < $height) {
      $new_width = ($new_height / $height) * $width;
    } else {
      $new_height = ($new_width / $width) * $height;
    }

    $newImg = $this->_CreateImg($new_width, $new_height, $type);
    imagecopyresampled($newImg, $img, 0, 0, 0, 0, $new_width, $new_height, $width, $height);
    return $newImg;
  }

<?php

/**
 * 图片处理，生成缩略图和添加水印图片
 * Created by PhpStorm.
 * User: andy
 * Date: 17-1-3
 * Time: 上午11:55
 */
class Image
{
 //原图
 private $imgPath; //图片地址
 private $width;  //图片宽度
 private $height; //图片高度
 private $type;  //图片类型
 private $img;  //图片(图像流)

 //缩略图
 private $newImg; //缩略图(图像流)
 private $newWidth;
 private $newHeight;

 //水印图路径
 private $waterMarkPath;

 //输出图像质量,jpg有效
 private $quality;

 /**
  * Image constructor.
  * @param string $imagePath 图片路径
  * @param string $markPath 水印图片路径
  * @param int $new_width 缩略图宽度
  * @param int $new_height 缩略图高度
  * @param int $quality JPG图片格输出质量
  */
 public function __construct(string $imagePath,
        string $markPath = null,
        int $new_width = null,
        int $new_height = null,
        int $quality = 75)
 {
  $this->imgPath = $_SERVER[&#39;DOCUMENT_ROOT&#39;] . $imagePath;
  $this->waterMarkPath = $markPath;
  $this->newWidth = $new_width ? $new_width : $this->width;
  $this->newHeight = $new_height ? $new_height : $this->height;
  $this->quality = $quality ? $quality : 75;

  list($this->width, $this->height, $this->type) = getimagesize($this->imgPath);
  $this->img = $this->_loadImg($this->imgPath, $this->type);


  //生成缩略图
  $this->_thumb();
  //添加水印图片
  if (!empty($this->waterMarkPath)) $this->_addWaterMark();
  //输出图片
  $this->_outputImg();
 }

 /**
  *图片输出
  */
 private function _outputImg()
 {
  switch ($this->type) {
   case 1: // GIF
    imagegif($this->newImg, $this->imgPath);
    break;
   case 2: // JPG
    if (intval($this->quality) < 0 || intval($this->quality) > 100) $this->quality = 75;
    imagejpeg($this->newImg, $this->imgPath, $this->quality);
    break;
   case 3: // PNG
    imagepng($this->newImg, $this->imgPath);
    break;
  }
  imagedestroy($this->newImg);
  imagedestroy($this->img);
 }

 /**
  * 添加水印
  */
 private function _addWaterMark()
 {
  $ratio = 1 / 5; //水印缩放比率

  $Width = imagesx($this->newImg);
  $Height = imagesy($this->newImg);

  $n_width = $Width * $ratio;
  $n_height = $Width * $ratio;

  list($markWidth, $markHeight, $markType) = getimagesize($this->waterMarkPath);

  if ($n_width > $markWidth) $n_width = $markWidth;
  if ($n_height > $markHeight) $n_height = $markHeight;

  $Img = $this->_loadImg($this->waterMarkPath, $markType);
  $Img = $this->_thumb1($Img, $markWidth, $markHeight, $markType, $n_width, $n_height);
  $markWidth = imagesx($Img);
  $markHeight = imagesy($Img);
  imagecopyresampled($this->newImg, $Img, $Width - $markWidth - 10, $Height - $markHeight - 10, 0, 0, $markWidth, $markHeight, $markWidth, $markHeight);
  imagedestroy($Img);
 }

 /**
  * 缩略图(按等比例,根据设置的宽度和高度进行裁剪)
  */
 private function _thumb()
 {

  //如果原图本身小于缩略图，按原图长高
  if ($this->newWidth > $this->width) $this->newWidth = $this->width;
  if ($this->newHeight > $this->height) $this->newHeight = $this->height;

  //背景图长高
  $gd_width = $this->newWidth;
  $gd_height = $this->newHeight;

  //如果缩略图宽高，其中有一边等于原图的宽高，就直接裁剪
  if ($gd_width == $this->width || $gd_height == $this->height) {
   $this->newWidth = $this->width;
   $this->newHeight = $this->height;
  } else {

   //计算缩放比率
   $per = 1;

   if (($this->newHeight / $this->height) > ($this->newWidth / $this->width)) {
    $per = $this->newHeight / $this->height;
   } else {
    $per = $this->newWidth / $this->width;
   }

   if ($per < 1) {
    $this->newWidth = $this->width * $per;
    $this->newHeight = $this->height * $per;
   }
  }

  $this->newImg = $this->_CreateImg($gd_width, $gd_height, $this->type);
  imagecopyresampled($this->newImg, $this->img, 0, 0, 0, 0, $this->newWidth, $this->newHeight, $this->width, $this->height);
 }


 /**
  * 缩略图(按等比例)
  * @param resource $img 图像流
  * @param int $width
  * @param int $height
  * @param int $type
  * @param int $new_width
  * @param int $new_height
  * @return resource
  */
 private function _thumb1($img, $width, $height, $type, $new_width, $new_height)
 {

  if ($width < $height) {
   $new_width = ($new_height / $height) * $width;
  } else {
   $new_height = ($new_width / $width) * $height;
  }

  $newImg = $this->_CreateImg($new_width, $new_height, $type);
  imagecopyresampled($newImg, $img, 0, 0, 0, 0, $new_width, $new_height, $width, $height);
  return $newImg;
 }

 /**
  * 加载图片
  * @param string $imgPath
  * @param int $type
  * @return resource
  */
 private function _loadImg($imgPath, $type)
 {
  switch ($type) {
   case 1: // GIF
    $img = imagecreatefromgif($imgPath);
    break;
   case 2: // JPG
    $img = imagecreatefromjpeg($imgPath);
    break;
   case 3: // PNG
    $img = imagecreatefrompng($imgPath);
    break;
   default: //其他类型
    Tool::alertBack(&#39;不支持当前图片类型.&#39; . $type);
    break;
  }
  return $img;
 }

 /**
  * 创建一个背景图像
  * @param int $width
  * @param int $height
  * @param int $type
  * @return resource
  */
 private function _CreateImg($width, $height, $type)
 {
  $img = imagecreatetruecolor($width, $height);
  switch ($type) {
   case 3: //png
    imagecolortransparent($img, 0); //设置背景为透明的
    imagealphablending($img, false);
    imagesavealpha($img, true);
    break;
   case 4://gif
    imagecolortransparent($img, 0);
    break;
  }

  return $img;
 }
}